DOCSLIB.ORG

Tunable Acoustic Double Negativity Metamaterial SUBJECT AREAS: Z

Total Page：16

File Type：pdf, Size：1020Kb

Download full-text PDF Read full-text
Tunable Acoustic Double Negativity Metamaterial SUBJECT AREAS: Z Tunable acoustic double negativity metamaterial SUBJECT AREAS: Z. Liang1, M. Willatzen2,J.Li1 & J. Christensen3 CONDENSED-MATTER PHYSICS FLUIDS 1Department of Physics and Materials Science, City University of Hong Kong, Tat Chee Avenue, Kowloon Tong, Hong Kong, 2Mads Clausen Institute, University of Southern Denmark, Alsion 2, DK-6400 Sønderborg, Denmark, 3IQFR - CSIC Serrano 119, 28006 MATERIALS SCIENCE Madrid, Spain. PHYSICS Man-made composite materials called ‘‘metamaterials’’ allow for the creation of unusual wave propagation Received behavior. Acoustic and elastic metamaterials in particular, can pave the way for the full control of sound in 16 August 2012 realizing cloaks of invisibility, perfect lenses and much more. In this work we design acousto-elastic surface modes that are similar to surface plasmons in metals and on highly conducting surfaces perforated by holes. Accepted We combine a structure hosting these modes together with a gap material supporting negative modulus and 11 October 2012 collectively producing negative dispersion. By analytical techniques and full-wave simulations we attribute the observed behavior to the mass density and bulk modulus being simultaneously negative. Published 14 November 2012 lassical waves such as sound and light have recently been put to the test in the challenges for cloaking objects1–8 and realizing negative refraction9–18. Those concepts are just a few of recent fascinating phe- Correspondence and nomena which are consequences of artificial electromagnetic (EM) or acoustic metamaterial designs. C 19 20 Perfect imaging or enhanced transmission of waves in subwavelength apertures are other disciplines within requests for materials the scope of metamaterials which have received considerable attention both from a theoretical and experimental should be addressed to point of view21–24. Smith et al. designed an EM composite material in which the electric and magnetic response act J.C. (johan. simultaneously to exhibit a negative effective index of refraction band25. The idea was to tune the resonance of a christensen@gmail. periodic array of split ring resonators such that the negative permeability would occur below the plasma fre- com) quency of a metallic rodded medium where the electric response is negative26,27. An advanced version of this design is provided by the so-called fishnet structure. In its various build-ups it contains a high figure-of-merit and gives rise to negative refraction in the near-IR10, microwave28 and optical regime13. Manipulating sound waves is readily possible by utilizing metamaterials. Those materials are realized by resonating building blocks that are fabricated on a size scale smaller than the wavelength of the irradiated acoustic wave. It is the ability to control and tune those meta-atoms, which forms the basics in the design for tailored and unusual acoustic material responses. There are different strategies in creating negative refraction using acoustic metamaterials. One approach is to use perforations. An isotropic negative index can be obtained by coiling up small channels of perforations17. Hyperbolic metamaterial for broad-angle negative refraction on the other hand, can be constructed using layered holey structures18. Another approach is to employ locally resonating structures. The first metamaterial fabricated to possess double negativity (simultaneous negative effective bulk modulus 1/k and mass density r) was a one-dimensional tube design consisting of periodic interspaced open side branches and membranes29. Both of those resonators describe a Drude-like behavior for the effective bulk modulus and mass density respectively. Results Designer acousto-elastic surface modes. To go beyond the lumped element design we introduce structured metallic components which are able to convey tunable double negativity behavior in a planar configuration although extensions into 3 dimensions should not add any difficulties. For the design of such a material we take a close look at the EM fishnet metamaterial and initially aim at converting its plasmonic interpretation into acousto-elasticity13. In its basic design we have two adjacent holey films made out of good conductors (Au, Ag) which are separated by a dielectric spacer. Metal surfaces punctured with subwavelength holes allow for the EM waves to penetrate much in the same way as a plasmon polariton30. Interestingly does the effective permittivity take the same plasma form whether they are supported in metals such as silver or in perforated highly conducting surfaces. It is this behavior which describes the electric response of a fishnet structure that is generated in the holey films. We will start out examining the acoustic analogy of these designer surface modes and SCIENTIFIC REPORTS | 2 : 859 | DOI: 10.1038/srep00859 1 www.nature.com/scientificreports Figure 1 | Transmittance and effective mass density spectra of the structured and elastically filled rigid screen. For all simulations, the normalized 3 screen thickness is fixed at h/dx 5 0.7 and the filling material has r 5 2300 kg/m and a longitudinal speed of sound cl 5 1410 m/s. Furthermore we 3 consider the sample to be immersed in water, c0 5 1481 m/s and r0 5 1000 kg/m . The transmittance (b) and effective mass density Re(reff) (c) spectra are calculated for ax/dx 5 0.5. In (d,e) we hold c0/ct 5 2. The full (dotted) lines represent data obtained by modal expansions (COMSOL simulation). The incident sound plane wave is impinging at the normal direction. (f) The band diagram is simulated for a structure with the parameters ax/dx 5 0.5 and h/dx 5 0.7 and contains filling parameters as in the latter example though with c0/ct 5 3.7. later study the effective bulk modulus which is showing resemblance localized, we fill these indentations with an elastic material as ren- to the magnetic response of the fishnet structure. dered in Fig. 1a. We begin with a simple model that is constructed for Let us suppose that we have a perfect rigid screen into which holes a structure with translational invariance in the y direction and tex- are carved. In order for an incident airborne sound field to be highly tured by periodic slits of lattice constant dx along the x axis. An SCIENTIFIC REPORTS | 2 : 859 | DOI: 10.1038/srep00859 2 www.nature.com/scientificreports incident wave excites elastic cavity modes inside the filled indenta- based on a retrieval technique31. The theoretical formalism used to tions which predominantly are governed by a displacement uz in the calculate the scattering coefficients is based on the modal expansion direction perpendicular to the lattice. The displacement generally of the pressure and velocity fields in free-space such as the displace- satisfies the homogeneous wave equation for an isotropic solid: ment and stresses inside the elastic inclusion32. Even though, in the former, the metamaterial halfspace is treated in the effective medium 2 2 2 2 2 L uz L uz L uz L uz L ux l ? r ~m z zðÞlzm z , ð1Þ limit ( ax) by solely introducing specular reflections and taking Lt2 Lz2 Lx2 Lz2 LxLz into account only the fundamental elastic cavity mode, we conduct simulations by considering all higher expansion orders. As given in where l, m and r are the modulus of incompressibility (first Lame´ the caption of Fig. 1, we hold the screen thickness h/dx that is normal- coefficient), modulus of rigidity (second Lame´ coefficient) and the ized to the lattice dx fixed, but vary the width ax/dx of the indentations solid mass density respectively. As the elastic inclusions are clamped and also the inclusion material by different values of the transversal 5 5 to the rigid frame, uz(x 0, ax) 0 must vanish at the edges of the speed of sound ct. Transmittance spectra are plotted and compared to slit. Furthermore, we must guarantee zero shear-stress at the free- the real part of the effective mass density Re(reff) as depicted in space and metamaterial interface as waves only propagate longit- Fig. 1b and Fig. 1c respectively. We clearly see that by lowering ct udinally in a fluid, sxz 5 0. Given the long wavelength limit which we also lower the onset of the first allowed band which means that ? we are mainly interested in, i.e., l ax, we take the fundamental the spectral locations of the acousto-elastic plasma frequencies cavity eigenmode to be dominant as it penetrates the deepest into the shift towards longer wavelengths l/dx. These are the locations at elastic inclusion, hence, we can write the out-of-plane displacement 2pc0 c0 lp~ ~2ax where the effective mass density, as seen in field inside this region as: vp ct p Fig. 1c, changes sign - the transition between an opaque and trans- ~ : : iwt uzðÞx,z A sinðÞbzz sin x e : ð2Þ parent effective fluid. Fig. 1d and Fig. 1e confirm that the acousto- ax elastic plasma oscillation can be further controlled by the indentation width a . With a specific chosen filling material, in this case c /c 5 Disregarding in-plane displacement (ux 5 0) is a plausible assump- x 0 t tion in narrow elastic channels, hence we substitute Eq. (2) into Eq. 2.0, we predict that the cut-off wavelengths now locate at lp 5 4ax.In order to verify the analytical approach based on modal expansions (1), whereupon we solve for the wavenumber bz comprising longit- udinal and transverse wave motion: (full lines in Fig. 1), we have further conducted full-wave simulations sffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffi sffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffi (COMSOL Multiphysics, dotted lines) and found very good agree- rffiffiffiffiffiffiffiffiffiffiffiffiffi ment. In addition we calculate the radiative transmittance band dia- r m p2 1 v v2 b ~v 1{ ~ 1{ p , ð3Þ gram which has been plotted in units of the plasma frequency. This is z z 2 2 2 l 2m r ax v cl v rendered in Fig.
Load more

Recommended publications
  • Plasma Oscillation in Semiconductor Superlattice Structure
    Memoirs of the Faculty of Engineering,Okayama University,Vol.23, No, I, November 1988 Plasma Oscillation in Semiconductor Superlattice Structure Hiroo Totsuji* and Makoto Takei* (Received September 30, 1988) Abstract The statistical properties of two-dimensional systems of charges in semiconductor superlattices are analyzed and the dispersion relation of the plasma oscillation is ealculated. The possibility to excite these oscillations by applying the electric field parallel to the structure is discussed. ]. Introduction The layered structure of semiconductors with thickness of the order of lO-6 cm or less is called semiconductor superlattice. The superlattice was first proposed by Esaki and Tsu [11 as a structure which has a Brillouin zone of reduced size and therefore allows to apply the negative mass part of the band structure to electronic devices through conduction of carriers perpendicular to the structure. The superlattice has been realized by subsequent developments of technologies such as molecular beam epitaxy (MBE) and metal-organic chemical vapor deposition (MOCVD) in fabricating controlled fine structures. At the same time, many interesting and useful physical phenomena related to the parallel conduction have also been revealed in addition to the parallel conduction. From the view point of application to devices, the enhancement of the carrier mobility due to separation of channels from Ionized impurities may be one of the most important progresses. Some high speed devices are based on this technique. The superlattlce structure
    [Show full text]
  • Carbon Fiber Skeleton/Silver Nanowires Composites with Tunable Negative
    EPJ Appl. Metamat. 8, 1 (2021) © Y. An et al., published by EDP Sciences, 2021 https://doi.org/10.1051/epjam/2020019 Available online at: epjam.edp-open.org Metamaterial Research Updates from China RESEARCH ARTICLE Carbon fiber skeleton/silver nanowires composites with tunable negative permittivity behavior Yan An1, Jinyuan Qin1, Kai Sun1,*, Jiahong Tian1, Zhongyang Wang2,*, Yaman Zhao1, Xiaofeng Li1, and Runhua Fan1 1 College of Ocean Science and Engineering, Shanghai Maritime University, Shanghai 201306, PR China 2 State Key Lab of Metal Matrix Composites, School of Materials Science and Engineering, Shanghai Jiao Tong University, Shanghai 200240, PR China Received: 13 November 2020 / Accepted: 25 December 2020 Abstract. With the development of periodic metamaterials, more attention has been paid to negative permittivity behavior due to great potential applications. In this paper, silver nanowires (AgNWs) were introduced to the porous carbon fibers (CFS) by an impregnation process to prepare CFS/AgNWs composites with different content of AgNWs and the dielectric property was investigated. With the formation of conductive network, the Drude-like negative permittivity was observed in CFS/AgNWs composites. With the increase of AgNWs, the connectivity of conductive network became enhanced, the conductivity gradually increases, and the absolute value of the negative dielectric constant also increases to 8.9 Â 104, which was ascribed to the enhancement of electron density of the composite material. Further investigation revealed that the inductive characteristic was responsible for the negative permittivity. Keywords: Negative permittivity / metacomposites / plasma oscillation / inductive characteristic 1 Introduction capacitors [10,11]. The electromagnetic metamaterials have a great value in the fields of wireless communication In the past decades, electromagnetic metamaterials with [12], electromagnetic absorption [13] and shielding [14], etc.
    [Show full text]
  • Free Electron Lasers and High-Energy Electron Cooling*
    FREE ELECTRON LASERS AND HIGH-ENERGY ELECTRON COOLING* Vladimir N. Litvinenko, BNL, Upton, Long Island, NY, USA# Yaroslav S. Derbenev, TJNAF, Newport News, VA, USA) Abstract The main figure of merit of any collider is its average Cooling intense high-energy hadron beams remains a luminosity, i.e., its average productivity for an appropriate major challenge in modern accelerator physics. branch of physics. Cooling hadron beams at top energy Synchrotron radiation of such beams is too feeble to may further this productivity. provide significant cooling: even in the Large Hadron For a round beam, typical for hadron colliders, the Collider (LHC) with 7 TeV protons, the longitudinal luminosity is given by a simple expression: ' * damping time is about thirteen hours. Decrements of N1N2 & s traditional electron cooling decrease rapidly as the high L = fc * % h) * , (1) 4"# $ ( # + power of beam energy, and an effective electron cooling of protons or antiprotons at energies above 100 GeV where N1, N2 are the number of particles per bunch, fc is seems unlikely. Traditional stochastic cooling still cannot their collision frequency, !* is the transverse !-function catch up with the challenge of cooling high-intensity at the collision point, " is the transverse emittance of the bunched proton beams - to be effective, its bandwidth b!ea m, #s is the bunch length, and h ! 1 is a coefficient must be increased by about two orders-of-magnitude. accounting for the so-called hourglass effect [1]: Two techniques offering the potential to cool high- " 1/ x 2 h(x) = e erfc(1/ x). energy hadron beams are optical stochastic cooling (OSC) x and coherent electron cooling (CEC) – the latter is the The hourglass effect is caused by variations in the beam’s 2 focus of this paper.
    [Show full text]
  • The Effect Pressure on Wavelengths of Plasma Oscillations in Argon And
    AN ABSTRACT OF TI-lE TRESIS OF - ¡Idgar for Gold.an the ri,, s. in (Name) (Degree) (Najor) Date Thesis presented ia. i9i__ Title flTO PSDEo LPLASMA OSeILLATIos..iN - Abstract Approved (-(Najor Professor) Experiments on argon and. nitrogen are described. which show that the wave length of electromaetjc radiation emitted from a gas plasma in a magnetic field is a function of the pressure of the gas. This result is Consistent with the theory of plasma oscillation developed by Tonics and Langniir if the assumption is made that plasma electron density is a function of gas pressure. A lower limit of wave length plasma of oscillation is indicated by the experiments in qualitative agreement with the Debye length equation, No difference in the wave length-tressn, relationship between the two gases was observed. The experimental tube, which consisted of a gas filled cylindrical anode with an axial tungsten filament) was motmted. in a magnetic field parallel to the axis of the anode. Gas pressures between i and 50 microns and. magnetic fields between 500 and 1,000 gauss were used. The anode voltage was aplied. in short pulses in order to mini- mize heating of the cathode by ion bombardment and to make possible the use of alternating voltage amplifiers in the receiver. The receiver of electromagnetic radiation consisted. of a crystal- detector dipole, constructed from a 1N26 crystal cartridge, followed by a video amp1ifier The amplifier had a maximum gain of 1.6 X iO7, and. a bandwidth of 2 megacycles Wave lengths were measured by means of an interferometer.
    [Show full text]
  • Introduction to Metamaterials
    FEATURE ARTICLE INTRODUCTION TO METAMATERIALS BY MAREK S. WARTAK, KOSMAS L. TSAKMAKIDIS AND ORTWIN HESS etamaterials (MMs) are artificial structures LEFT-HANDED MATERIALS designed to have properties not available in To describe the basic properties of metamaterials, let us nature [1]. They resemble natural crystals as recall Maxwell’s equations M they are build from periodically arranged (e.g., square) unit cells, each with a side length of a. The ∂H ∂E ∇×E =−μμand ∇×H = εε (1) unit cells are not made of physical atoms or molecules but, 00rr∂tt∂ instead, contain small metallic resonators which interact μ ε with an external electromagnetic wave that has a wave- where the r and r are relative permeability and permit- λ ⎡ ∂ ∂ ∂ ⎤ length . The manner in which the incident light wave tivity, respectively, and L =⎢ ,,⎥ . From the above ⎣⎢∂xy∂ ∂z ⎦⎥ interacts with these metallic “meta-atoms” of a metamate- equations, one obtains the wave equation rial determines the medium’s electromagnetic proper- ties – which may, hence, be made to enter highly unusual ∂2E ∇=−2E εμεμ (2) regimes, such as one where the electric permittivity and 00rr∂t 2 the magnetic permeability become simultaneously (in the ε μ same frequency region) negative. If losses are ignored and r and r are considered as real numbers, then one can observe that the wave equation is ε The response of a metamaterial to an incident electromag- unchanged when we simultaneously change signs of r and μ netic wave can be classified by ascribing to it an effective r . (averaged over the volume of a unit cell) permittivity ε ε ε μ μ μ To understand why such materials are also called left- eff = 0 r and effective permeability eff = 0 r .
    [Show full text]
  • Plasma Waves
    Plasma Waves S.M.Lea January 2007 1 General considerations To consider the different possible normal modes of a plasma, we will usually begin by assuming that there is an equilibrium in which the plasma parameters such as density and magnetic field are uniform and constant in time. We will then look at small perturbations away from this equilibrium, and investigate the time and space dependence of those perturbations. The usual notation is to label the equilibrium quantities with a subscript 0, e.g. n0, and the pertrubed quantities with a subscript 1, eg n1. Then the assumption of small perturbations is n /n 1. When the perturbations are small, we can generally ignore j 1 0j ¿ squares and higher powers of these quantities, thus obtaining a set of linear equations for the unknowns. These linear equations may be Fourier transformed in both space and time, thus reducing the differential equations to a set of algebraic equations. Equivalently, we may assume that each perturbed quantity has the mathematical form n = n exp i~k ~x iωt (1) 1 ¢ ¡ where the real part is implicitly assumed. Th³is form descri´bes a wave. The amplitude n is in ~ general complex, allowing for a non•zero phase constant φ0. The vector k, called the wave vector, gives both the direction of propagation of the wave and the wavelength: k = 2π/λ; ω is the angular frequency. There is a relation between ω and ~k that is determined by the physical properties of the system. The function ω ~k is called the dispersion relation for the wave.
    [Show full text]
  • Simulating Twistronics in Acoustic Metamaterials
    Simulating twistronics in acoustic metamaterials S. Minhal Gardezi,1 Harris Pirie,2 Stephen Carr,3 William Dorrell,2 and Jennifer E. Hoffman1, 2, ∗ 1School of Engineering and Applied Sciences, Harvard University, Cambridge, MA, 02138, USA 2Department of Physics, Harvard University, Cambridge, MA, 02138, USA 3Brown Theoretical Physics Center and Department of Physics, Brown University, Providence, RI, 02912-1843, USA (Dated: March 24, 2021) Twisted van der Waals (vdW) heterostructures have recently emerged as a tunable platform for studying correlated electrons. However, these materials require laborious and expensive effort for both theoretical and experimental exploration. Here we numerically simulate twistronic behavior in acoustic metamaterials composed of interconnected air cavities in two stacked steel plates. Our classical analog of twisted bilayer graphene perfectly replicates the band structures of its quantum counterpart, including mode localization at a magic angle of 1:12◦. By tuning the thickness of the interlayer membrane, we reach a regime of strong interlayer tunneling where the acoustic magic angle appears as high as 6:01◦, equivalent to applying 130 GPa to twisted bilayer graphene. In this regime, the localized modes are over five times closer together than at 1:12◦, increasing the strength of any emergent non-linear acoustic couplings. INTRODUCTION cate, acoustic metamaterials have straightforward gov- erning equations, continuously tunable properties, fast 1 Van der Waals (vdW) heterostructures host a di- build times, and inexpensive characterization tools, mak- verse set of useful emergent properties that can be cus- ing them attractive testbeds to rapidly explore their tomized by varying the stacking configuration of sheets quantum counterparts. Sound waves in an acoustic meta- of two-dimensional (2D) materials, such as graphene, material can be reshaped to mimic the collective mo- other xenes, or transition-metal dichalcogenides [1{4].
    [Show full text]
  • Recent Advances in Acoustic Metamaterials for Simultaneous Sound Attenuation and Air Ventilation Performances
    Preprints (www.preprints.org) | NOT PEER-REVIEWED | Posted: 27 July 2020 doi:10.20944/preprints202007.0521.v2 Peer-reviewed version available at Crystals 2020, 10, 686; doi:10.3390/cryst10080686 Review Recent advances in acoustic metamaterials for simultaneous sound attenuation and air ventilation performances Sanjay Kumar1,* and Heow Pueh Lee1 1 Department of Mechanical Engineering, National University of Singapore, 9 Engineering Drive 1, Singapore 117575, Singapore; [email protected] * Correspondence: [email protected] (S.K.); [email protected] (H.P.Lee) Abstract: In the past two decades, acoustic metamaterials have garnered much attention owing to their unique functional characteristics, which is difficult to be found in naturally available materials. The acoustic metamaterials have demonstrated to exhibit excellent acoustical characteristics that paved a new pathway for researchers to develop effective solutions for a wide variety of multifunctional applications such as low-frequency sound attenuation, sound wave manipulation, energy harvesting, acoustic focusing, acoustic cloaking, biomedical acoustics, and topological acoustics. This review provides an update on the acoustic metamaterials' recent progress for simultaneous sound attenuation and air ventilation performances. Several variants of acoustic metamaterials, such as locally resonant structures, space-coiling, holey and labyrinthine metamaterials, and Fano resonant materials, are discussed briefly. Finally, the current challenges and future outlook in this emerging field
    [Show full text]
  • What Is Plasma? Its Characteristics Plasma Oscillations Plasmon And
    Topics covered here are: What is Plasma? Its Characteristics Plasma Oscillations Plasmon and plasmon frequency Sources used here are: http://farside.ph.utexas.edu/teaching/plasma/Plasmahtml/node1.html https://www.britannica.com/science/plasma-state-of-matter/Plasma-oscillations- and-parameters What is Plasma The electromagnetic force is generally observed to create structure: e.g., stable atoms and molecules, crystalline solids. Structured systems have binding energies larger than the ambient thermal energy. Placed in a sufficiently hot environment, they decompose: e.g., crystals melt, molecules disassociate. At temperatures near or exceeding atomic ionization energies, atoms similarly decompose into negatively charged electrons and positively charged ions. These charged particles are by no means free: in fact, they are strongly affected by each others' electromagnetic fields. Nevertheless, because the charges are no longer bound, their assemblage becomes capable of collective motions of great vigor and complexity. Such an assemblage is termed a plasma. Of course, bound systems can display extreme complexity of structure: e.g., a protein molecule. Complexity in a plasma is somewhat different, being expressed temporally as much as spatially. It is predominately characterized by the excitation of an enormous variety of collective dynamical modes. Its occurrence and characteristics Since thermal decomposition breaks interatomic bonds before ionizing, most terrestrial plasmas begin as gases. In fact, a plasma is sometimes defined as a gas that is sufficiently ionized to exhibit plasma-like behavior. Note that plasma-like behavior ensues after a remarkably small fraction of the gas has undergone ionization. Thus, fractionally ionized gases exhibit most of the exotic phenomena characteristic of fully ionized gases.
    [Show full text]
  • Theoretical Study of Subwavelength Imaging by Acoustic Metamaterial
    Theoretical study of subwavelength imaging by acoustic metamaterial slabs Ke Deng1,2, Yiqun Ding1, Zhaojian He1, Heping Zhao2, Jing Shi1, and Zhengyou 1,a) Liu 1Key Lab of Acoustic and Photonic materials and devices of Ministry of Education and Department of Physics, Wuhan University, Wuhan 430072, China 2Department of Physics, Jishou University, Jishou 416000, Hunan, China We investigate theoretically subwavelength imaging by acoustic metamaterial slabs immersed in the liquid matrix. A near-field subwavelength image formed by evanescent waves is achieved by a designed metamaterial slab with negative mass density and positive modulus. A subwavelength real image is achieved by a designed metamaterial slab with simultaneously negative mass density and modulus. These results are expected to shed some lights on designing novel devices of acoustic metamaterials. a)To whom all correspondence should be addressed, e-mail address is [email protected] 1 I. INTRODUCTION Recent advances in electromagnetic (EM) metamaterials (MMs)1 provide the foundation for realizing many intriguing phenomena, such as inverse Doppler Effect,2 negative refraction,3 and amplification of evanescent waves.4 These phenomena can be utilized to design novel EM devices. Pendry found that, as the combined result of negative refraction and amplification of evanescent waves, a MM slab with effective permittivityε =−1 and permeability μEM = −1 can focus both the propagating and evanescent waves of a point source into a perfect image.5 Thereby such a slab device has been referred as the perfect lens. Pendry’s perfect lens stimulated lots of research interests due to the great significance of subwavelength imaging in various applications (see the ref.
    [Show full text]
  • Acoustic Velocity and Attenuation in Magnetorhelogical Fluids Based on an Effective Density Fluid Model
    MATEC Web of Conferences 45, 001 01 (2016) DOI: 10.1051/matecconf/201645001 01 C Owned by the authors, published by EDP Sciences, 2016 Acoustic Velocity and Attenuation in Magnetorhelogical fluids based on an effective density fluid model Min Shen1,2 , Qibai Huang 1 1 Huazhong University of Science and Technology in Wuhan,China 2 Wuhan Textile University in Wuhan,China Abstract. Magnetrohelogical fluids (MRFs) represent a class of smart materials whose rheological properties change in response to the magnetic field, which resulting in the drastic change of the acoustic impedance. This paper presents an acoustic propagation model that approximates a fluid-saturated porous medium as a fluid with a bulk modulus and effective density (EDFM) to study the acoustic propagation in the MRF materials under magnetic field. The effective density fluid model derived from the Biot’s theory. Some minor changes to the theory had to be applied, modeling both fluid-like and solid-like state of the MRF material. The attenuation and velocity variation of the MRF are numerical calculated. The calculated results show that for the MRF material the attenuation and velocity predicted with this effective density fluid model are close agreement with the previous predictions by Biot’s theory. We demonstrate that for the MRF material acoustic prediction the effective density fluid model is an accurate alternative to full Biot’s theory and is much simpler to implement. 1 Introduction Magnetorheological fluids (MRFs) are materials whose properties change when an external electro-magnetic field is applied. They are considered as “smart materials” because their physical characteristics can be adapted to different conditions.
    [Show full text]
  • Finite-Element Design of Metamaterial Beams For
    FINITE-ELEMENT DESIGN OF METAMATERIAL BEAMS FOR BROADBAND WAVE ABSORPTION _______________________________________ A Thesis presented to the Faculty of the Graduate School at the University of Missouri-Columbia _______________________________________________________ In Partial Fulfillment of the Requirements for the Degree Master of Science _____________________________________________________ by SHUYI JIANG Dr. P. Frank Pai, Thesis Supervisor MAY 2015 The undersigned, appointed by the Dean of the Graduate School, have examined the thesis entitled FINITE-ELEMENT DESIGN OF METAMATERIAL BEAMS FOR BROADBAND WAVE ABSORPTION Presented by Shuyi Jiang A candidate for the degree of Master of Science And hereby certify that in their opinion it is worthy of acceptance. Professor P. Frank Pai Professor Steven Neal Professor Stephen Montgomery-Smith ACKNOWLEDGEMENTS I would like to express my deepest appreciation to my advisor Dr. P. Frank Pai. Without his patient guidance, I wouldn’t have grown as a good researcher. His continuous encouragement and valuable suggestions on my thesis work meant a lot to me. Also I would like to thank my committee members, Dr. Steven Neal and Dr. Stephen Montgomery-Smith, for serving on my thesis committee and providing me assistance when I have difficulties. I would also like to extend my thanks to Dr. Hao Peng, Xuewei Ruan, Haoguang Deng, Yiqing Wang, Jamie Lamont and all my labmates. They helped my study and gave me confidence to reach the goal. Thanks to all the staff in the Mechanical and Aerospace Engineering Department for their hard work for me during my study at the University of Missouri. Finally, special thanks to my family for their mental and financial support through my life.
    [Show full text]